1. Field of the Invention
This invention relates to an alternator for a vehicle such as a passenger automotive vehicle or a truck.
2. Description of the Related Art
To reduce the aerodynamic resistance during traveling, a vehicle body tends to be formed into a slant nose shape. Securing a sufficient residential space for a passenger compartment is earnestly demanded. To satisfy these requirements, engine rooms of automotive vehicles have recently become so narrow and crowded that only a limited space is available for installing an alternator. Meanwhile, as vehicular engine noises have been lowered, there have been demands for the reduction in vehicular alternator noises. Thus, a compact, high-power, and low-noise alternator for a vehicle is required to be provided at a low cost.
One way of enabling a compact design and a high power output of an alternator for a vehicle is to improve the cooling performance of a stator winding by having the greatest heat loss.
FIG. 13 shows a prior-art alternator having a fan-built-in structure in which cooling fans are disposed in an alternator frame to apply cooling winds directly to coil ends to cool them. The prior-art alternator of FIG. 13 has the following problem. In the prior-art alternator of FIG. 13, since the cooling fans are opposed to only tip portions of coil end groups of a stator winding, cooling winds generated by rotation of the cooling fans are applied to only the tip portions of the coil end groups before being discharged. Thus, the effect of cooling the stator winding is relatively weak.
Japanese published unexamined utility-model application 5-11769 (corresponding to U.S. Pat. No. 5,233,255) discloses an alternator for a vehicle in which coil end groups of a stator winding extend axially so as to be sufficiently opposed to cooling fans. The alternator of Japanese application 5-11769 has the following problems. In the alternator of Japanese application 5-11769, since base portions of the coil end groups are not opposed to the cooling fans, the effect of cooling the base portions of the coil end groups is relatively weak. Since the coil end height is great, the resistance of the stator winding increases and thus an alternator power output decreases.
In general, it is known that an increase in area exposed to a cooling wind and an increase in flow rate of the cooling wind improve the cooling performance.
In a fan-built-in alternator for a vehicle, inner circumferential surfaces of a coil end group are rugged since multiple-phase windings are located there while being overlapped in a circumferential direction. Such an alternator has the following problem. A collision between a cooling wind and the rugged surfaces increases a periodical pressure variation, thereby causing greater fan noise.
Japanese published unexamined patent application 8-308190 (corresponding to U.S. Pat. No. 5,543,676) discloses an alternator in which the height of a coil end group and the height of a cooling fan are approximately equal in an axial direction, and the coil end group and the cooling fan are opposed to each other. The alternator of Japanese application 8-308190 has the problem that a collision of a cooling wind and rugged inner circumferential surfaces of the coil end group increases fan noise.